1. Field of the Invention
The present invention generally relates a vehicle steering control apparatus for a steer-by-wire system provided with a clutch for mechanically connecting and disconnecting a driver operating unit configured to be operated by a driver and a steering unit configured to steer a steered wheel to and from each other.
2. Background Information
In conventional steer-by-wire (SBW) systems in which the steering wheel and the steering mechanism of the front wheels are mechanically separated from each other, a clutch is provided as a backup mechanism for mechanically connecting the steering wheel and the steering mechanism. When a problem (failure) occurs in a portion of the SBW system, the clutch is connected immediately and the SBW control is aborted. If, for example, the reaction force actuator fails, once the steering wheel starts moving due to operation by the driver, the steering wheel will rotate easily until the clutch is completely engaged. Also until engagement of the clutch, a normal steering actuator will continue to operate in accordance with the rotary operation of the steering wheel, i.e., in accordance with the steering wheel angle value detected by a steering wheel angle sensor. Thus, the steered wheels may turn much more sharply than the driver intends causing an undesirable vehicle behavior. In order to prevent the undesirable vehicle behavior, the control gain of the steering actuator is lowered or set to zero for a prescribed amount of time in order to restrict the operation of the steering actuator during the period from when the failure is detected until the clutch is connected. The prescribed amount of time is set in advance to a value that accurately reflects the time required for the clutch to connect (engage). The prescribed amount of time is determined by experimentally measuring the clutch engagement (connection) time and using, for example, the largest value from among a plurality of data. One example of this type of conventional vehicle steering control apparatus is disclosed in Japanese Laid-Open Patent Publication No. 2005-096745).
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved vehicle steering control apparatus. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.